8. The nuclear model The Planetary Model of the Atom
• Their Is a nucleus at the centre of the atom.
• Protons and neutrons are accumulated in the
• The nucleus is positively charged
• Electrons revole around the nucleus
• The number of electrons in an atom is equal to the
number of protons.
• the atom is electrically neutral.
This atomic model was introduced by
Ernest Rutherford in 1911
9. Bohr Model of the Atom
• Niels Bohr further elaborated the
According to Bohr Model ,
• The electrons move in definite paths or
shells around the positively charged
10. Energy levels
• There are four main energy levels or shells
around the nucleus .
• They are assigned either numbers 1, 2, 3, 4......
or letters K, L, M, N...... respectively starting
from the nearest to the nucleus.
• Each energy level has a specific energy
• When moving away from the nucleus this
energy increases. Nevertheless, the
difference between the energy levels
11. • In an atom, there is a maximum number of
electrons in any energy level.
12. Atomic number
The atomic number is the number of
protons in an atom of the element.
Atomic number = number of protons
symbol of the elemant
13. Mass number
The sum of the number of protons and
neutrons in the nucleus of an atom is
called the mass number
mass number = number of protons + number of neutrons
symbol of the element